Quantum Key Distribution Network With Injection-Locked PIC Lasers
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Solution Overview
Problem
Existing quantum key distribution systems face challenges in achieving compact, cost-effective, and efficient implementation of twin-field QKD due to the complexity and cost of off-chip lasers, broad linewidths of on-chip lasers, and the need for additional hardware like phase-locked loops.
Innovation Solution
The use of on-chip secondary lasers with optical injection locking (OIL) between a primary and secondary lasers, integrated on photonic integrated circuits (PICs), which enables global phase coherence, suppresses side modes, and eliminates the need for external splitters and circulators, allowing for compact and lower-cost nodes with precise wavelength locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If on-chip secondary lasers are used, then device complexity and cost are reduced, but linewidth broadening occurs
Solution Approach 1:
A primary laser acts as an intermediary to optically injection-lock the secondary on-chip lasers. The primary laser's narrow linewidth serves as a reference that suppresses the broader linewidth of the secondary lasers through optical injection locking, achieving both compact integration and precise wavelength control
Solution Approach 2:
The linewidth parameter of the secondary lasers is changed from broad (inherent to on-chip lasers) to narrow (locked to primary laser) through optical injection locking. This parameter transformation allows the system to maintain the compactness of on-chip lasers while achieving the spectral precision required for quantum key distribution
2Manufacturing precision
If off-chip lasers are used, then linewidth precision is improved, but device complexity and cost increase
Solution Approach 1:
Instead of using expensive off-chip lasers, the patent uses inexpensive on-chip lasers that are optically injection-locked to a primary laser. The secondary lasers effectively 'copy' the spectral properties of the primary laser through optical injection locking, achieving wavelength precision without the cost and complexity of off-chip components
Solution Approach 2:
The patent replaces the mechanical/optical alignment systems and phase-locked loops traditionally needed for wavelength stabilization with optical injection locking. This substitution eliminates complex feedback control mechanisms while achieving stable wavelength locking through the natural physics of optical injection
3Stability of the object's composition
If phase-locked loops and external splitters are used, then phase coherence is maintained, but device complexity increases
Solution Approach 1:
The patent replaces electronic phase-locked loops with optical injection locking. The phase coherence is maintained through the optical coupling mechanism itself rather than through electronic feedback control, eliminating the need for complex electronic stabilization systems
Solution Approach 2:
The patent merges the functions of phase stabilization, wavelength locking, and laser generation into a single optical injection locking mechanism. This consolidation eliminates the need for separate phase-locked loops, external splitters, and circulators, achieving phase coherence with reduced hardware complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration achieves compact, cost-effective, and efficient quantum key distribution by enabling global phase coherence, narrowing linewidths, and reducing hardware complexity, thereby facilitating high-yield production and efficient single-photon interference measurements.
Implementation Method 1
Optical injection locking (OIL) is a widely used technique in laser systems, in fields including quantum communication. Optical injection locking generally involves a primary laser and secondary laser. For example, light from the primary laser may be used to define the phase between pulses output by the secondary laser.
Implementation Method 2
the interference unit is configured to perform single-photon interference measurements on light received from the secondary lasers
Data Source
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Figure 3A~3D
AI summary
A quantum key distribution (QKD) system is disclosed having a primary node and at least two secondary nodes. The primary node includes a primary laser and an interference unit. Each secondary node includes a secondary laser on a photonic integrated circuit (PIC), as well as an encoder that encodes quantum states onto light emitted by the secondary laser. The secondary lasers are configured to be injected by light from the primary laser in an optical injection locking scheme. The interference unit is configured to perform single-photon interference measurements on light received from the secondary lasers. An accompanying method is also disclosed.